fix: time shift not working with fill gaps (#7999)

pkg/query-service/postprocess/gaps.go

@@ -19,7 +19,7 @@ func StepIntervalForFunction(params *v3.QueryRangeParamsV3, query string) int64
 	return q.StepInterval
 }
 
-func fillGap(series *v3.Series, start, end, step int64) *v3.Series {
+func fillGap(series *v3.Series, start, end, step, shiftBy int64) *v3.Series {
 	v := make(map[int64]float64)
 	for _, point := range series.Points {
 		v[point.Timestamp] = point.Value
@@ -28,6 +28,8 @@ func fillGap(series *v3.Series, start, end, step int64) *v3.Series {
 	// For all the values from start to end, find the timestamps
 	// that don't have value and add zero point
 	start = start - (start % (step * 1000))
+	start += shiftBy * 1000
+	end += shiftBy * 1000
 	for i := start; i <= end; i += step * 1000 {
 		if _, ok := v[i]; !ok {
 			v[i] = 0
@@ -65,8 +67,11 @@ func FillGaps(results []*v3.Result, params *v3.QueryRangeParamsV3) {
 		if builderQueries != nil {
 			// The values should be added at the intervals of `step`
 			step := StepIntervalForFunction(params, result.QueryName)
+			shiftBy := builderQueries[result.QueryName].ShiftBy
+			start := params.Start - shiftBy*1000
+			end := params.End - shiftBy*1000
 			for idx := range result.Series {
-				result.Series[idx] = fillGap(result.Series[idx], params.Start, params.End, step)
+				result.Series[idx] = fillGap(result.Series[idx], start, end, step, shiftBy)
 			}
 		}
 	}

pkg/query-service/postprocess/gaps_test.go

@@ -178,14 +178,59 @@ func TestFillGaps(t *testing.T) {
 				}),
 			},
 		},
+		{
+			name: "Single series with gaps and time shift",
+			results: []*v3.Result{
+				createResult("query1", []*v3.Series{
+					createSeries([]v3.Point{
+						{Timestamp: 1747597560000, Value: 2.0}, // 19 May 2025 1:16:00 AM
+					}),
+				}),
+			},
+			params: &v3.QueryRangeParamsV3{
+				Start: 1747595100000, // 19 May 2025 12:35:00 AM
+				End:   1747599000000, // 19 May 2025 1:40:00 AM
+				CompositeQuery: &v3.CompositeQuery{
+					PanelType: v3.PanelTypeGraph,
+					BuilderQueries: map[string]*v3.BuilderQuery{
+						"query1": {
+							StepInterval: 840, // 14 minutes
+							QueryName:    "query1",
+							Expression:   "query1",
+							ShiftBy:      3600, // 1 hour
+						},
+					},
+				},
+			},
+			expected: []*v3.Result{
+				createResult("query1", []*v3.Series{
+					createSeries([]v3.Point{
+						{Timestamp: 1747595040000, Value: 0.0}, // 19 May 2025 12:34:00 AM
+						{Timestamp: 1747595880000, Value: 0.0}, // 19 May 2025 12:48:00 AM
+						{Timestamp: 1747596720000, Value: 0.0}, // 19 May 2025 1:02:00 AM
+						{Timestamp: 1747597560000, Value: 2.0}, // 19 May 2025 1:16:00 AM
+						{Timestamp: 1747598400000, Value: 0.0}, // 19 May 2025 1:30:00 AM
+					}),
+				}),
+			},
+		},
 	}
 
 	// Execute test cases
 	for _, tt := range tests {
 		t.Run(tt.name, func(t *testing.T) {
 			FillGaps(tt.results, tt.params)
+			if len(tt.results) != len(tt.expected) {
+				t.Errorf("Test %s failed: expected %d results, got %d", tt.name, len(tt.expected), len(tt.results))
+			}
 			for i, result := range tt.results {
+				if len(result.Series) != len(tt.expected[i].Series) {
+					t.Errorf("Test %s failed: expected %d series, got %d", tt.name, len(tt.expected[i].Series), len(result.Series))
+				}
 				for j, series := range result.Series {
+					if len(series.Points) != len(tt.expected[i].Series[j].Points) {
+						t.Errorf("Test %s failed: expected %d points, got %d", tt.name, len(tt.expected[i].Series[j].Points), len(series.Points))
+					}
 					for k, point := range series.Points {
 						if point.Timestamp != tt.expected[i].Series[j].Points[k].Timestamp ||
 							point.Value != tt.expected[i].Series[j].Points[k].Value {